Coordination Polymers Constructed from an Adaptable Pyridine-Dicarboxylic Acid Linker: Assembly, Diversity of Structures, and Catalysis

4,4′-(Pyridine-3,5-diyl)dibenzoic acid (H2pdba) was explored as an adaptable linker for assembling a diversity of new manganese(II), cobalt(II/III), nickel(II), and copper(II) coordination polymers (CPs): [Mn(μ4-pdba)(H2O)]n (1), {[M(μ3-pdba)(phen)]·2H2O}n (M = Co (2), Ni (3)), {[Cu2(μ3-pdba)2(bipy)]·2H2O}n (4), {[Co(μ3-pdba)(bipy)]·2H2O}n (5), [Co2(μ3-pdba)(μ-Hbiim)2(Hbiim)]n (6), and [M(μ4-pdba)(py)]n (M = Co (7), Ni (8)). The CPs were hydrothermally synthesized using metal(II) chloride precursors, H2pdba, and different coligands functioning as crystallization mediators (phen: 1,10-phenanthroline; bipy: 2,2′-bipyridine, H2biim: 2,2′-biimidazole; py: pyridine). Structural networks of 1–8 range from two-dimensional (2D) metal–organic layers (1–3, 5–8) to three-dimensional (3D) metal–organic framework (MOF) (4) and disclose several types of topologies: sql (in 1), hcb (in 2, 3, 5), tfk (in 4), 3,5L66 (in 6), and SP 2-periodic net (6,3)Ia (in 7, 8). Apart from the characterization by standard methods, catalytic potential of the obtained CPs was also screened in the Knoevenagel condensation of benzaldehyde with propanedinitrile to give 2-benzylidenemalononitrile (model reaction). Several reaction parameters were optimized, and the substrate scope was explored, revealing the best catalytic performance for a 3D MOF 4. This catalyst is recyclable and can lead to substituted dinitrile products in up to 99% product yields. The present study widens the use of H2pdba as a still poorly studied linker toward designing novel functional coordination polymers.


Figure S4
Typical 1 H NMR spectra of the reaction mixtures (and product yield calculation) p. S8

Figure S5
Accumulation of product vs. time in the Knoevenagel condensation p. S14

Scheme S1
Plausible mechanism for the Knoevenagel condensation reaction catalyzed by 4 p. S15

Table S1
Selected bond lengths and angles for compounds 1-8 p. S16

Table S2
Hydrogen bonds in crystal packing of 1-8 p. S17 Table S3 Reaction attempts for the synthesis of CPs p. S18 Table S4 Porosity and gas sorption data for 4 p. S19

S6
S7 Figure S2. PXRD patterns of compounds 1-8 at room temperature. Black patterns correspond to the experimental data obtained using the as-synthesized bulk samples. Red patterns were simulated from the single crystal X-ray data (CIF files). Blue patterns are those after the water treatment experiment (the samples were kept in water at 50 °C for 12 h, then isolated and dried before PXRD measurements). Figure S3. X-ray photoelectron spectroscopy (XPS) spectrum of 6. The ratio of Co 2+ and Co 3+ peak areas is 1.07:1 (by peak deconvolution). Percentage of the unreacted substrate: 0/1.00 = 0% Conversion of 2-nitrobenzaldehyde = yield of (2-nitrobenzylidene)malononitrile = 100−0 = 100%.

S13
Product yield calculation in the Knoevenagel condensation reaction. The -CH peak of 4-methylbenzaldehyde (substrate) appears at 9.96 ppm while that of (4-methylbenzylidene)malononitrile (product) can be seen at 7.73 ppm.

Product yield calculation in the Knoevenagel condensation reaction. The -CH peak of 4-methoxybenzaldehyde
(substrate) appears at 9.89 ppm while that of (4-methoxybenzylidene)malononitrile (product) can be seen at 7.66 ppm.

S14
Product yield calculation in the Knoevenagel condensation reaction. The -CH peak of 4-hydroxybenzaldehyde (substrate) appears at 9.87 ppm while that of (4-hydroxybenzylidene)malononitrile (product) can be seen at 7.64 ppm.